Radio receiver



0d. 1940. L. WALSH Re. 21,598

RADIO RECEIVER Original Filed March 5, 1934 4 Sheets-Sheet l INVENTOR Z/IVCDZ/V Was/l A'ITORN EY I Re. 21,598

Oct. 8, 1940. L. WALSH RADIO RECEIVER Original Filed March 5, .1334 4 Sheets-Shoat 2 V INVENTOR Z/m'oz/v WM s HPE p onvcy FREQUENCY ATTORNEY 0&8, 1940.

L... WALSH RADIO RECEIVER I Original Filedflarch 5, 1934 Rel 21,598

4 Sheets-Sheet 5 INVENTOR wcou M1 51% ZKM .ATI'ORNEY L. WALSH RADIO RECEIVER Oct. v& 1946.

4 Sheets-Shae t 4 Origihal Filed March 5. 19:54

mvENToR J/mcou M15 "ATTORNEY Rama oasis 4 Re. 21,598

UNITED STATES PATENT OFFICE Original No. 2,037,445, dated April 14, 1936, Serial No. 714,037, March 5, 1934. Application for reissue April 21, 1937, Serial No. 138,192

9 Claims. (01. 250-20)- This invention relates to radio receiving sysside bands the less the selectivity. But the tems and apparatus and has to do more especially broader the side bands passed without excessive with superheterodyne receivers. attenuation the fineris the possible tone quality Because of the fact that the frequency separaand, conversely, the narrower the side bands 5 tion between broadcasting channels is only ten passed without excessive attenuation the poorer 5 kilocycles, whereas the frequency band essential .the possible tone quality. Because the purchas-. to high fidelity is of the order of sixteen kilocycles, ing public is prone to judge a receiver by its abilit follows that high selectivity (which is necesity to bring in distant stations, it is believed to sary for satisfactory long distance reception) is have been universally considered necessary in incompatible with fine tone quality. That is to commercial broadcast receivers to design the in- 10 say, with the existing ten kilocycle channel sepatermediate frequency amplifiers to cut off sharply ration, it is impossible to secure at one and considerably below ten kilocycles on either side the same time both sharp selectivity and a high of the intermediate carrier frequency in order to degree of tone fidelity. preserve the requisite'degree of selectivity for dis- The type of broadcast receiving circuit in most tant reception. This, of course, definitely limitgeneral use at the present time is the superheteroed the quality of reproduction to the best obtaindyne. This is due in large measure to the .fact able without the higher frequencies even when that the superheterodyne is inherently capable receiving from local stations under conditions not of sharp selectivity and more constant selectivrequiring sharp selectivity. It is true that tone ill)v ity over the entire broadcast band without incurfidelity of a fairly high order and satisfactory for rence of the difficulties which ordinarily accommany purposes can be realized in the absence of pany the realization of comparable selectivity the higher frequencies, but there is, nevertheless, with other types of broadcast receiving circuits. a vast difference between what can be accom- With the superheterodyne, as with' other receiving plished with afrequency band limited as in the 26 systems, sharpselectiv'ity and fine tone quality past and that which can be accomplished with a cannot obtain simultaneously; and, insofar as I band wide enough to include all the desirable have been able to ascertain, there has, heretofore, audio frequencies-that is, up to, say, sixteen never been devised a superheterodyne receiver 'cakilocycles. v

pable of sharp selectivity for distant reception "Broadly, one of the major features of the pres- 80 (that is, for, reception of weak signal waves) and ent invention is the provision in a superhetero- 3o relatively broad selectivity for reception from dyne receiver, of an intermediate frequency amless distant stations (that is, strong signal waves) plifier wherein the width ofthe side bands capable whereby is obtainable the maximum tone quality of being passed without over-attenuation is variconsistent with the momentarily necessary degree able at the will of the operator. This is accom- 36 of selectivity. That, in brief, is the major object plished'without altering. or at least, without maof the present invention; which is to say, to proterially altering the resonance frequency to which vide a superheterodyne receiver wherein the the interstage couplings are tuned and prefersha rpness of selectivity is easily and quickly varably by varying the interstage coupling at one or iable, to the end that fine tone quality may be more of the intermediate amplifier coupling cir- 4o realized whenever sharp tuning is not necessary cults or between the intermediate frequency am- 0 and, conversely, that sharp selectivity may be plifier and the second detector-preferably both. realized whenever interference between transmit- There are numerous possible and more or less ting stations would otherwise obtain. practicable alternative arrangements within the In superheterodyne receivers selectivity is sescope and purview of the presently considered 5' cured chiefly in the intermediate frequency amfeature-as will later be evident to those familiar plifier wherein the interstage coupling circuits with this art-but the arrangement which I have are sharply tuned to some predetermined interso far found most desirable consists in providing mediate frequency value -generally one hunmeansfor simultaneously varying the coupling in dred and seventy-five kiio'cycles. These amplithree successive tuned-transformer coupling cirfiers, as heretofore designed and constructed, will cults in the intermediate amplifier and between 50 pass the intermediate frequency and a relatively that amplifier and the second detector-the in-.- narrow side-band on either side thereof without ductive coupling between primary and secondary excessive attenuation. The narrower the side windings being preferably adjustable by the operbands permitted to pass the greater is the selecator.

as tivity of the receiver and conversely the wider the Another feature-subordinate to that just 5 previously mentioned-consists in an arrangement to be described whereby a certain compensating effect is accomplished as between the several successive coupling circuits to the end that all frequencies within the band intended to be passed are transmitted with substantially equal attenuation, thereby achieving a degree of tone fidelity which would not otherwise be obtainable. :KIhis result is brought about by providing for a predetermined difference in coupling variation as between different successive coupling circuits so that frequencies disproportionately attenuated in one or more stages are correspondingly underattenuated in another stage-the over-all resultant being that all frequencies within the desired band are passed with substantially equal facility-hence with an absence of material distortion.

For the purpose of diminishing the effective noise resulting from extraneous electrical disturbances such as static and the whistle due to the heterodyning of interfering stations it is desirable to providein the receiver an adjustable audio-frequency filter, the cut-oil pointof which can be adjusted, as needed, to-eliminate the higher frequencies. The use of such a filter for the Purpose stated is not novel, per se, and is not claimed of itself as a part of this invention; but I have discovered that the optimum adjustments of such filters under varying circumstances bear a' very definite relation to the optimum adjustments of the intermediate frequency amplifier under croresponding conditions and this hasled to the further discovery that it is practicable to mechanically tie together the filter adjusting means and the intermediate frequency amplifier adjusting means so that by the operation of a single control medium, both adjustments are effected simultaneously-411m greatly simplifying the operation of the receiver, This constitutes another important feature of the present invention. Still another feature of this invention consists in a novel method of tuning the intermediate frequency coupling systems; and this is applicable alike to receivers having variably coupled intermediate frequency coupling systems in accordance with the present invention and to receivers wherein the coupling is fixedin conformity with the prior practice.

These coupling systems consist each of a pair of inductively coupled tunable circuits, each of which is intended to be tuned to the intermediate frequency, and the coupling therebetween is, of necessity, greater than what is known as critical coupling. If less than critical coupling were employed the band of frequencies passed would be too narrow for good reproduction. But with coupling greater than critical the tunable circuits making up each pair react upon each other so that the tuning of either changes the tuning of the other-:which makes it difficult to get the individual tunable circuits tuned accurately to the intermediate frequency. I have discovered that by loosening the coupling to a point below critical coupling and then adjusting each circuit to the intermediate frequency the problem of tuning is greatly simplified and thatmuch time may thus be saved. And that applies with equal force whether the coupling is to be variable in operation according to the present invention or I fixed in accordance with prior established prac- Il referencetothe Additional features of this invention are to be found in novel structural ents which will be described in detail hereinafter with Referring to the drawings:

Fig. l is a'circuit diagram of so much of a radio receiving system as is essential to illustrate the present invention;

Figs. 2, 3. 4, and 5 respectively, are resonance curves pertaining to the intermediate frequency coupling systems;

Fig. 6 is a. plan view, partly in section, of a radio receiver chassis; I

Fig. 7 is a rear elevational view, partly in section, of the same chassis; I

Fig. 8 is a horizontal sectional view taken approximately along the line 8-8 of Figs. 7 and 9; and

Fig.' 9 is a cross sectional view taken along the line 9-9 of Figs. 6 and 8.-

The circuit diagram, Fig. 1, is intended to illustrate schematically the novel features of the present invention applied to an otherwise more or less conventional superheterodyne broadcast receiver.

It is thought unnecessary to describe in extensive detail the entire circuit illustrated or to dwell at length upon the well known principles of operation of superheterodyne receivers. It seems appropriate, however, to describe rather briefly the whole system illustrated as a background for a more detailed description of the novel features to which the appended claims are directed.

Referring to Fig. 1, numeral l designates as an entirety the receiving antenna, including series resistances 2, 3, and 4'the antenna being grounded at 5. Associated with the antenna isa multi-contact rotary antenna switch 6, the function of which is to change the point of connection of the receiver to the antenna for the purpose of increasing and diminishing the effectiveness of the antenna; or, putting it another way, for the P pose of increasing and diminishing the amount of antenna voltage applied to the input end of the receiver. In general, it is desirable, if not necessary, to set the antenna switch for maximum voltage for the reception of very weak signals whereas for the reception of strong signals it is desirable to reduce the antenna voltage in order to eliminatedistortion due to over loading of the tubes.

A conductor 1 extends from the movable contact of antenna switch 6 to one end of the primary winding 8 of a radio frequency input transformer 9.

The incoming signal waves are impressed through the medium of primary winding I upon the input side of a vacuum tube I. which functions as a radio frequency amplifier'for the incoming high frequency signal wave. The circuit connections immediately with the amplifier tube II are more or less conventional and familiar to those skflled in this art for which reason it is thought that it would be superfluous to burden this specification with a detailed description of them.

Following the radio frequency amplifier tube II is a second vacuum tube II which may properly be referred'to as a converter, translator, or

first detectorthese terms being used more or less interchangeably in the art with respect to the case illustrated, generated by a high freu quency -vacuum tube oscillator which is here designated as a whole by reference numeral I3, This local oscillator is of a conventional type requiring no description and is inductively coupled to a coil I4 in the input or control circuit of the converter tube ll.

The frequency generated by the local oscillator I3 is always different from that of the incoming high frequency wave by an amount equal to some predetermined fixed value-w'hich value is now most generally, but not always, one hundred and seventy-five kilocycles. That is to say, whatever frequency the-receivermay be tuned to receive at any given time, the local oscillator generates a frequency which is different therefrom by one hundred and seventy-five kilocycles-or whatever other value may have been determined 'upon by the designer of the set.

Assuming that the predetermined beat or intermediate frequency is one hundred and seventyfive kilocycles, the output circuit, comprising the transformer primary winding II and tuning condenser l6, is tuned to that frequency.

Following the converter tube II are shown two intermediate or beat frequency amplifier tubes, I1 and I8 respectively. The input side of tube I1 is coupled with the output side of tube I I through the medium of a coupling transformer l9 comprising primary winding l5 and a secondary winding 20. The primary winding l5, as already stated, is tuned by means of the condenser l6 to one hundred and seventy-five kilocycles and the secondary 20 is tuned by means of a condenser'2l to the same frequency. According to this invention windings l5 and 20 are relatively movable so as to vary the inductive coupling, that is to say, the degree of coupling therebetween. Although both the primary and secondary of transformer I9 are individually tuned to the intermediate frequency they will, if closely coupled, pass not only the beat frequency but also a considerable band of frequencies to either side thereof. In fact it is essential, as stated at the beginning of this specification, that a frequency band up to about sixteen kilocycles on each side of the carrier be passed in order to make possible reproduction of all the desirable tone frequencies. But, as already explained, a wide frequency band isincompatible with sharp selectivitythis being due to the fact that broadcast channel separation is only ten kilocycles. It would clearly not be possible at all to separate stations of comparable signal strength operating on' adjacent frequency channels with a receiver adjusted to pass a band of frequencies even as high as ten kilocycles.

The width of the band of frequencies passed by the interstage coupling system comprising primary and secondary windings l5 and 20 depends upon the degree of coupling between them. With loose coupling the frequency band is greatly narrowed, whereas, with tight coupling it is broadened.

It is not practicable with a single coupling system such as that under discussion to secure both sufficiently sharp selectivity and a broad frequency band with anything like a close approximation to uniform attenuation of all frequencies within the desired band. This is graphically illustrated in Fig.2 wherein A represents a resonance curve for loose coupling and B represents a resonance curve for close coupling-the abscissae representing frequency and the ordinates representing amplitude. It will be seen that according to curve B the carrier or intermediate frequency is greatly attenuated as compared .with the side-band frequencies to either side thereof.

This is an inherent condition as a result of which, it will be apparent, there could not be obtained with a single coupling systemof the kind illustrated a satisfactory wide frequency band-except by introducing resistance into the circuit and thus impairing its selectivity. The present invention, however, cures this defect by compensating for it as will presently be explained.

Between intermediate amplifier tubes l1 and I8 is a second coupling system identical with that just described comprising a coupling transformer 22 consisting of a primary winding 23 and a secondary winding 24 which are tuned each to one hundred and seventy-five kllocycles by condensers 25 and 26 respectively. The resonance characteristics of this coupling system are illustrated graphically by Fig. 3 which as will be seen is identical with Fig. 2. 7

Following the second intermediate frequency amplified tube I8 is a full wave diode rectifier tube 21 which functions as a detector to-convert the amplified beat frequency wave into an audible frequency current corresponding to the signalmodulations 'of the incoming high frequency wave. The interstage coupling between the output side of the last intermediate frequencyamplifier tube l8 and-the detector 21 is of the same form as the coupling systems previously described, comprising as it does a coupling transformer 28 consisting of a primary 29 with tuning condenser 30 and secondary 3| with tuning condenser 32.

In each of the three successive interstage coupling systems to which-reference has been made the primary and secondary windings are spacially adjustable with respect to one another for varying the degree of coupling therebetween and mechanical means to be described later are provided for effecting these adjustments simultaneously. The adjustments of the first two successive coupling systems, that is to say, the coupling system between tubes II and I1 and between tubes l1 and II may be assumed to be identical as illustrated graphically by Figs. 2 and 3 respectively; but the coupling adjustment mechanism to be hereinafter described is so designed as to bring about a different degree of relative movement of the primary and secondary windings of the interstage coupling comprising transformer 28. This is illustrated graphically by Fig. 4 wherein A: depicts the resonance curve for loose coupling and B: depicts the resonance curve for close coupling.

It will be observed that curve B: is considerably broader at the top than curve A; but is not as broad as curves B and B1. However, curve B: dips but little at the midpoint corresponding to the intermediate frequency whereas curves B and B1 indicate a very great attenuation of the intermediate frequency and the side band frequencies immediately to either side thereof. I

, Fig. 5 illustrates graphically the effect of combining the three coupling systems in cascade.

Here A: and B3 are the resultant resonance curves for loose coupling and close coupling respectively.

- From an examinationof these graphs it will be seen that by reason of the looser maximum coupling maintained in one of the coupling systems as illustrated by Fig. 4 there isachieved a resultant broad frequency band of approximately uniform. amplitude for all frequencies included therein which is illustrated by the resonance curve Ba.

The graphs of Figs. 2, 3, 4, and 5 are illustrative of only two coupling adjustments, one of these being the adjustment for very sharp selectivity ductance coils, I6, 31, 38, in series, and four sets of shunt capacities, 39, ll, II, and 42. Each of these sets of shunt capacities may comprise, as illustrated, a group of condensersof respectively different capacities which are capable of being cut into circuit individually by the movable contactorsJlJl, 48,. I

The function of filter fl is to eflecta sharp cutoff of the higher audible frequencies whenever this is necessary in order to reduce or eliminate 7 noise and/or the heterodyne whistle whichsometimes occurs due to the presence of interfering carrier waves having an audible frequency difference.

When receiving from nearby stations-pr more distant powerful stations it is not usually necessary to suppress'noise because the signal is generally so strong as to completely obscure it; and for that reason it is neither necessary nor desirable,

under those circumstances. to suppress thehigher frequencies. and the filter should accordingly be- -adjusted to be ineflective. As, however, the desired signals become increasingly weak, noise be- 'comes increasingly objectionable on account of being more and more noticeable.- The constituent noise-frequencies within the same band as the reproduced signal frequenciescannot of course be byfiltering because the filter will not distinmiish between noise and signal of the same But, as stated at the outset, the sigfrequencies than is the noise and for that reason a very much betterover-all result'can be accomplished by impairing the si n l through 'elimination of the higher frequencies and at the same time diminishing the noise by eliminating the same noise frequencies. In order this and get the o mum balance between noise and signal for different degrees of signalistrength it is desirable to have a filter which is adjustable to several cutoff points. In the arrangement'ill'ustrated mm. 1 the switches II to ll inclusive have-six points of adjustment. Whether or notit is necessary to provide as many filter adjustments as this is a matter of engineering judgment and a point which may be here as largely irrelevant.

In addition to the multi-contact switches which have already been referred to, there is still another designated by reference numeral 41. This switch is interposed in one of the filter input 'leadsanditsonlypurposeistoopenthecircuit concurrently with the opening of the other switches thereby preventing a clicking noise in the loudspeaker.

As previously stated, I have discovered that the optimum adjustment of the audio-filter bears in each instance a definite relation to the coupling adjustment of the intermediate frequency amplifier and I have found it to be practicable and desirable to mechanically tie together the several multi-contact switches of the filter and the means for adjusting the coupling of the intermediate frequency transformers. Also I have observed that the appropriate adjustment of the antenna This filter as shown comprises three inswitch 8 is definitely related to the intermediate frequency coupling adjustment and that of the filter, wherefore it is also practicable and desirable to arrange for operating the antenna switch simultaneously with the filter switches and the coupling adjusting means.

The output terminals of the audio-filter may be and are usually connected through a volume control to the input terminals of a power amplifier where the signals are amplified sufiiciently to operate a suitable loudspeaker. The power amplifier and loudspeaker, however, have nothing to do with the present invention and for that reason have not been, illustrated in the circuit diagram.

Included in the circuit diagram, Fig. 1, is an automatic volume control-identified as a whole by reference numeral 12 and comprising an amplifier tube I3 and a diode rectifier 14. This feature is now too well known in the art to require a detailed description and it has no immediate and necessary bearing on the invention claimed. There is, however, a feature, believed to be novel, which is related to the invention claimed and which works in close conjunction with theautomatic volume control andis thought worthy of special mention. What is'referred to v is the indicator or meter IS-which may be anordinary D. C. milliammeterthe function 6: which will b explained. As depicted by curve B: of Fig. 5,'when the intermediate frequency systems are adjusted for close coupling,

ness obtains thatis not true of the tone quality.

Quality of tone is badly impaired if the receiver i is off tune to any considerable extent.-this being nal is less impaired by elimination of the higher due to, inequality of side bands.

The control grid of the automatic volume control amplifier tube If is connected through conductor ll to one terminal of secondary IQ of the second adjustable. coupling system, and since at close coupling there are two voltage peaks at either side of the beat frequency carrien these are impressed upon the control grid of-tube ll givingrise to corresponding current peaks in the circuit ofdiode rectifier 14,. in one-branch of which is included, in series, the indicator or meter Il.1The meter or other current responsive indicating device will, accordingly, give peak readings at each of two points equally distant from and at either side of the correct position of the tuning dial whenever a signal is picked up. This renders it easy for the operator to tune correctly in each instance .and'thereby obtain maximum tone quality when receiving sufiiciently strong signals to enable the use of close coupling.

There are numerous elements included in the circuit diagram, Fig. 1,. of which no specific men-- tion has been made. These are all conventional and familiar elements of a modern superheterodyne broadcast receiver as will be readily observed by those skilled in the art and it is thought that nothing would specification with a detailed description thereof.

Figs. 6, '1, 8, and 9 illustrate a complete superheterodyne broadcast receiver chassis. Many of be gained by burdening this a frequency band'of'considerablewidth is passed the elements shown have no immediate bearing on the present invention and the only reason for showing them is to illustrate their physical relation to those parts which are relevant to the invention. Those parts, therefore, which are not tact members of the rotary gang switch ,of shorter radius than cranks 64. and 65.

strictly essential to the disclosure have been shown in comparatively light lines thereby emphasizing the essential components.

The parts shown in Figs. 6 to 9 inclusive to which particular attention is to be directed are three transformer units, 48. 49, and 50 respectively, a rotary gang switch 5|, a crank shaft 52, a connecting link 53, a switch shaft 54, and a cam 55. Each of the transformer units 48, 49, and 50 comprises, asits major constituents, a primary transformer winding 56 and'a secondary transformer winding 51 together with a pair of small adjustable condensers 58 corresponding to the condensers l5, 2|, 25, 26, 30 and 32 on the circuit diagram, Fig. 1. The primary windings are stationarily mounted on a cross-head of insulating material 59 which in turn is adjustably mounted on a pair of threaded rods 60 and BI. The secondary windings 51 aremounted on cross-heads of insulating material 52 which are slotted so as to slidably engage the rods 50 and 6| whereby to permit vertical movement of the secondary windings relatively to the primary windings, thus effecting variations in the degree of coupling between primaries and secondaries. The three cross-heads 62 are connected by means of connecting rods 53 to crankarms 64, 65, and 66, re.- spectively, which, in turn, are mounted upon and rotatable. with shaft 52, these cranks serve to move the secondary windings toward and away from theprlmary windings in response to arcuate rotation of shaft 52 as will be evident from an examination of Fig. '1. Shaft 52 is rotated arcuately by link 53 which is connected at one end to crank 51 and at the other end to a cam groove 55a in the cam member 55. A link 68 fulcrumed at 59 is pivotally connected to one end of link 53.

Link 68 serves to support one end of link 53 while at the same time permitting that end to move horizontally in response to rotation of cam 55.

The retractile spring serves to hold the cam follower on link 53 tightly in contact with one face of the cam groove thereby avoiding backlash in the mechanism.

Cam plate 55 is mounted on shaft 54 and rotatable therewith asis likewise the movable con- This gang switch is made up of the six multi-contact switches indicated in F18. 1.

A control knob ll designed for manual operation is connected. to shaft 54, manipulation of which, as will be apparent, effects simultaneous adjustment of the six multi-contact switches and the three intermediate frequency transformers.

As explained with reference to the circuit diagram, Fig. 1, and the resonance curves Figs. 2 to 5 inclusive, the coupling variation in one of the three intermediate frequency coupling systems is less than that of the other two-the reason as explained being to bring about the desired compensatory effect thereby accomplishing an approximately uniform attenuation of all frequencies within a wide band as illustrated by resonance curve B: of Fig. 5. This is accomplished in the mechanism shown by making the crank 66 The vertical movement of the secondary winding of transformer unit 50 is, therefore, less than that of units 45 and 49the result being that the maximum coupling attainable in transformer unit 5|! is less than the maximum coupling attainable in either of the other two transformer units.

As may be observed from an inspection of Fig. 9 for example. the transformer windings of units 45, 49; and 50 are capable of being quite widely ing the coupling systems is to loosen the coupling between the primaries and secondaries in all three coupling systems, to a point below critical coupling, insert a 'micro-ammeter in the common leg of the rectifier circuit of diode 21 and then with the intermediate amplifier in operation receiving a signal wave of one hundred'and seventyfive kilocyclesfrom a signal generator, adjusting each tuned circuit of the coupling systems, one

by one, to that frequency until a maximum reading is obtained on the aforementioned mlcroammeter. When all have been thus tuned the couplings can be readjusted, as required, to secure the broader resonance band, without disturbing the tuning.

It is, of'course, necessary to exercise good engineering judgment and skill in order to carry out this invention and realize the best possible results, but the information herein set forth is believed to be entirely sufficient to enable those skilled in the art to do so.

It will be evident that there are numerous possible alternative mechanical arrangements for effecting the simultaneous adjustments as herein described but the specific arrangement illustrated is found to be a very convenient and economical one.

I have illustrated and described what I believe to be the best electrical and mechanical arrangements for carrying out this invention but I realize that there are many possible variations and modifications within the scope and purview of the inventive concept and I accordingly do not wish the invention to be regarded as limited except as indicated by the appended claims.

What is claimed is:

1. A radio receiving system comprising, in combination, a source of signal-modulated high frequency incoming waves, a local source of high frequency waves for beating with the incoming signal waves, means for combining said waves to produce a signal-modulated beat frequency wave,

means for converting said beat frequency wave into a signal wave of audio-frequency, an adjustable coupling system interposedbetween said first mentioned means and said second mentioned means, said coupling system being designed to pass only a relatively narrow band of frequencies including the beat frequency but having means for rendering adjustable the width of the band passed, an audio-frequency low-pass filter having its input connected to said second mentioned means, said filter being provided with means for adjustably varying the point of cut-off thereof,

' and means common to said coupling system and said filter for effecting the aforementioned atl-v justments in unison. 2. A superheterodyne receiver including a frequency converter, an intermediatefrequency am-' plifier, an intermediate frequency detector, and a low-pass filter connected to said. detector, a plurality of coupling systems in cascade interposed between said frequency converter and said detector, each of said coupling systems being de-' signed to pass a relatively narrow band of frequencies including the intermediate frequency and having means rendering adjustable the width of the effective frequency band passed thereby, said filter including means for adjusting its point of cut-off, and means common to said coupling systems and said filter for effecting the aforementioned adjustments in unison.

3. In a superheterodyne receiver, a source of signal-modulated high frequency incoming waves, a local source of high frequency waves for beating with the incoming signal waves, a translator for combining said waves to produce a signal-modulated intermediate frequency wave, an intermediate frequency amplifier including, in combination, a plurality of transformer units, each having a stationary winding and a movable winding inductively coupled thereto, and a coupling adiusting mechanism common to said units and operable to effect movement of said movable windings in unison, said mechanism comprising a crankshaft having a plurality of crank arms, links connecting said movable windings with said crank arms individually, a rotatable cam for driving said crankshaft and driving means connecting said cam and crankshaft,- and a detector operable 5. In a superheterodyne radio receiver having separate means for selection and amplification at radio. frequency, intermediate frequency and audio frequency, means for varying the band widths v at at least one carrier frequency, tone control means for v r-vine the cut-oi! at audio frequency, and sinsle control means forv operating said varying means in coordination and in unison with said tone control means.

6. In a radio receiver having variable carrier frequency selecting means, demodulating means and separate variable audio frequency selecting means, single control means varying the width of the band passed by the carrier frequency selecting means in unison and in coordination with tone control means varying the audio frequency cut-01f.

7. In combination in a radio receiver, variable cut-oil audio frequency tone control means, variable band width carrier frequency selective means, and single control means for operating the tone control means and adjusting the width of the band passedby thecarrier frequency selective means inproportion to the cut-off period of the tone control means.

8. A carrier frequency receiver having carrier frequency selectors whose passed band width is variable, audio frequency filters whose passed frequency characteristic is variable, and single control means for the passed band width and passed frequency characteristic simultaneously and in predetermined nr i rtion to one another. I I

9. In a superheterodyne receiver having a radio frequencyampiifleriwith tuned input and output circuits, an intermediate frequency amplifler with tuned coupling transformers and an audio frequency amplifier with filter circuits for varying the frequency response characteristic thereof, single control means for varying the selective characteristics of the intermediate frequency coupling transformers in unison and coordination with the audio frequency filter circuit variations.

Lmcom wsnsn, 

